DC Navy Yard shooter's mother: 'My heart is broken'

The Washington Navy Yard, site of Monday's mass shooting where 13 died, including the gunman, remained closed Wednesday. (Source: CNN)

Aaron Alexis entered the Washington Navy Yard with a shotgun and killed 12 people Monday before dying in a shootout with responders, according to police. (Source: FBI/CNN)

(RNN) - The mother of Aaron Alexis, the man who killed 12 people in the Washington Navy Yard shooting, said Wednesday she is "glad" her son can do no more harm to anyone.

"Our son, Aaron Alexis, has murdered 12 people and wounded several others," Cathleen Alexis said in a statement from her Brooklyn, NY, home. "His actions have had a profound, everlasting effect on the families of the victims. I don't know why he did what he did, and I'll never be able to ask him why."

She told the victims' families she was "so, so very sorry this has happened."

"My heart is broken," she said.

CNN reported two engravings etched into the shotgun Alexis used. The etchings read "better off this way" and "my elf weapon," though it's not entirely clear what either etching means.

On Wednesday, the Department of Veterans Affairs confirmed Alexis was treated twice in the month of August for insomnia. On both occasions, the VA says Alexis was "alert and oriented and was asked by VA doctors if he was struggling with anxiety or depression, or had thoughts about harming himself or others, all of which he denied."

A police report obtained by CNN shows that Alexis told police on Aug. 7 that he was hearing voices and thought people were following him, sent to "keep him awake by talking to him and sending vibrations into his body" while he was staying at a Rhode Island hotel.

Alexis "stated that the individuals are using 'some sort of microwave machine' to send vibrations through the ceiling, penetrating his body so he cannot fall asleep."

The report goes on to say Alexis claimed he had no history of mental illness in his family and that he has never had any sort of "mental episode."

The site of the mass shooting that killed 12 people remained closed Wednesday to all but essential personnel as the official investigation went on.

Questions remained as to why Aaron Alexis, a former Navy reservist with chronicled gun-related incidents and mental issues, was allowed clearance to enter the base.

Alexis opened fire at about 8:20 a.m. Monday at the Naval Sea Systems Command building, killing civilians who worked on the base and injuring eight others before dying in a firefight with police.

In the wake of the incident, Navy Secretary Ray Mabus ordered two reviews of the Navy's security clearance and screening procedures Tuesday. President Barack Obama also ordered a similar review for contractors and employees across the federal government, according to the Associated Press.

Law enforcement officials, who identified Alexis through fingerprints, said he worked for Hewlett Packard as a subcontractor for the Navy. They said investigators had not yet found a manifesto or other writings to suggest a motive for the killings.

CNN reported investigators believe Alexis may have smuggled an unassembled pump-action shotgun into the Naval complex in a backpack and assembled it in a restroom. Investigators also believe the shooter used buckshot during the incident.

Among the dead named Monday were Michael Arnold, 59; Sylvia Frasier, 53; Kenneth Proctor, 46; and Kathleen Gaarde, 63. Also killed were 73-year-old John Roger Johnson, 61-year-old Vishnu Pandit and 50-year-old Frank Kohler. None of them were military personnel.

Officials said Alexis came to Washington, DC, on Aug. 25 and had been staying in hotels in the days before the shooting.

Benita Bell, who met the gunman last week, told CNN she saw his demeanor change as the week progressed.